Problem: Solve for $a$ : $6 = a + 25$
Subtract $25$ from both sides: $ \begin{eqnarray} \\ \hphantom{6 {- 25}} &\hphantom{=}& \hphantom{a} \\ 6 &=& a + 25 \\ \\ {-25} && {-25} \\ \end{eqnarray} $ $ \begin{eqnarray} \\ 6 {- 25} &=& a \\ \end{eqnarray} $ Simplify. $ a = -19$